Neuronal splicing and plasticity of the synaptic connections
Despite the extremely complex processes that steer axonal growth, the number of the synapses that are created during embryonic development is substantially higher than the number of synapses in the fully mature nervous system. Thus a considerable part of the originally formed neuronal connections is doomed to disappear. This process of the selective elimination commences before birth and continues into adulthood, thus lasting for a long time.
The transformation processes of the neuronal connections depend on the synaptic capacity of the neurons. Indeed, each neuron develops a predetermined number of synapse on its dendrites and its cell body. In the initial phase of cell development the synaptic capacity is thus the largest and it decreases during neuronal maturing. In their work on the striated cortex of young macaques Rakic and Bourgeois have shown that the synaptic capacity diminishes dramatically within 2 years (by roughly 50%).
The neuromuscular connection offers a useful model for illustrating the synaptic fine tuning. Originally, each muscle fiber is innervated by the axons of more numerous neurons. When maturation is complete, each muscle fiber is furnished with only a single neuron.